9 reds in a 125g?

[jp80911]

Im still kinda new to the hobby. What do you mean by "footprint"?

The term footprints that he's refering to is asking the measurements of the tank. Essentially if the 125 and 150 have the same width and length, there's not much of an advantage of getting the larger one since piranhas don't necessarly need the heigth.

Correct, standard 125 gallon tank is 72" long and 18" wide which is the same as standard 150 gallon tank only it's taller and that's where the extra gallon come from.
for piranhas the length and width of the tank is more important than height as piranhas don't swim up and down that much.

Click here and you can find the dimensions of most of the standard size tanks.